Effects of H{sub 2} enrichment on the propagation characteristics of CH{sub 4}-air triple flames

Journal Article · Thu May 15 00:00:00 EDT 2008 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2008.02.005· OSTI ID:21036808

Briones, Alejandro M; Aggarwal, Suresh K ^[1]; Katta, Viswanath R ^[2]

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1. Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL 60607 (United States)
2. Innovative Scientific Solutions, Inc., 2766 Indian Ripple Road, Dayton, OH 45440 (United States)

The effects of H{sub 2} enrichment on the propagation of laminar CH{sub 4}-air triple flames in axisymmetric coflowing jets are numerically investigated. A comprehensive, time-dependent computational model, which employs a detailed description of chemistry and transport, is used to simulate the transient ignition and flame propagation phenomena. Flames are ignited in a jet-mixing layer far downstream of the burner. Following ignition, a well-defined triple flame is formed that propagates upstream along the stoichiometric mixture fraction line with a nearly constant displacement velocity. As the flame approaches the burner, it transitions to a double flame, and subsequently to a burner-stabilized nonpremixed flame. Predictions are validated using measurements of the displacement flame velocity. As the H{sub 2} concentration in the fuel blend is increased, the displacement flame velocity and local triple flame speed increase progressively due to the enhanced chemical reactivity, diffusivity, and preferential diffusion caused by H{sub 2} addition. In addition, the flammability limits associated with the triple flames are progressively extended with the increase in H{sub 2} concentration. The flame structure and flame dynamics are also markedly modified by H{sub 2} enrichment, which substantially increases the flame curvature and mixture fraction gradient, as well as the hydrodynamic and curvature-induced stretch near the triple point. For all the H{sub 2}-enriched methane-air flames investigated in this study, there is a negative correlation between flame speed and stretch, with the flame speed decreasing almost linearly with stretch, consistent with previous studies. The H{sub 2} addition also modifies the flame sensitivity to stretch, as it decreases the Markstein number (Ma), implying an increased tendency toward diffusive-thermal instability (i.e. Ma {yields} 0). These results are consistent with the previously reported experimental results for outwardly propagating spherical flames burning a mixture of natural gas and hydrogen. (author)

• OSTI ID: 21036808
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 3 Vol. 153; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABUNDANCE
AIR
AXIAL SYMMETRY
COMBUSTION KINETICS
COMPUTERIZED SIMULATION
CORRELATIONS
DIFFUSION
Diffusive-thermal instability
ENRICHMENT
FLAME PROPAGATION
FLAMMABILITY
HYDROGEN
Hydrogen-methane blends
IGNITION
INSTABILITY
LAMINAR FLAMES
MATHEMATICAL MODELS
METHANE
MIXING
MIXTURES
Preferential diffusion
Propagating triple flames
SENSITIVITY
STOICHIOMETRY
Stretch-flame speed interactions
TIME DEPENDENCE
TRANSIENTS
VELOCITY